Multi-Phase Interferometer

An optical perturbation sensing system, comprising:

• a probing beam incident on a medium with perturbations;
• a sensing beam redirected from said medium and incident on a surface area of a photodetector;
• a reference beam directed onto the photodetector surface to form, with the sensing beam, an interference pattern on the photodetector surface;
• a phase patterner with at least two phase regions across its section, to generate different phases in different regions of said interference pattern;
• an array of photodetector elements, to detect each phase region of the interference pattern;
• and
• a constructive combiner for constructively combining detected signals from said elements, to form a stronger detected signal with reduced intensity noise, reduced background noise, and reduced sensitivity to phase drifts;
• the constructive combiner being adapted to subtract pairs of said detected signals, square the subtracted signal squares, and sum up said squared signals.